Process for recycling of tungsten carbide alloy

ABSTRACT

The present disclosure is a process for the recycling of tungsten carbide alloy. Tungsten carbide alloy scrap is heated in an oxidizing atmosphere and the oxidized material is pulverized by grinding. The powder material is treated with a carburizing mixture for reducing and carburizing the powdered tungsten oxides and other metal oxides. The method is cost effective and environment friendly.

TECHNICAL FIELD

The present disclosure belongs to the recycling of a metal alloy. In particular the disclosure relates to a method of recycling of tungsten carbide alloy. The method is cost effective and environment friendly in nature.

BACKGROUND

A huge quantity of tungsten carbide scraps are generated by machine shops, oil exploration companies and the manufacturers of machine tools as worn out inserts and rejections.

Presently the scraps are being recycled by following methods-by regrinding of inserts. This method has limited application as beyond a certain point, it is not possible to regrind them. Chemical methods are also available for the recycling of the scraps. This involves oxidation of the scrap followed by alkali leaching to convert the scrap into sodium tungstate from which raw tungsten will be recovered. Another method involves fusion using sodium nitrite or sodium nitrate as oxidizing agent, sodium carbonate as the diluent to recover tungsten compounds. This method requires high temperature in the process of extraction. The scraps are also recycled by zinc process which yields the tungsten carbide powder directly. But this is a costly process and requires huge investment. Other processes like leach milling, acid leaching and electrolysis. Inspite of the availability of various methods about 35% of the scraps are not recycled for want of capacity.

Hence there is a need for a cost effective process for the extraction of the tungsten carbide.

STATEMENT OF DISCLOSURE

Accordingly the present disclosure provides a process for recycling of tungsten carbide alloy comprising acts of oxidizing the tungsten carbide alloy to obtain tungsten oxide and other metallic oxides, grinding the tungsten oxide and other metallic oxides to obtain a powder and treating the powder with a carburizing gaseous mixture for reducing and carburizing the tungsten oxide and other metallic oxide powder to obtain the purified tungsten carbide alloy powder.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The features of the present disclosure will become more fully apparent from the following description taken in conjunction with the accompanying drawings. Understanding that the drawings depict only several embodiments in accordance with the disclosure and are therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

FIG. 1 illustrates the process of recycling of tungsten carbide alloy in a flowchart.

FIG. 2 is the micro structure of the recycled powder from example 1 analyzed by EDS method.

FIG. 3 is the graph showing the quantity of electrons diffracted by the particular element during EDS studies from the powder recycled from example 1.

FIG. 4 is the micro structure of the recycled powder from example 2 analyzed by EDS method.

FIG. 5 is the graph showing the quantity of electrons diffracted by the particular element during EDS studies from the powder recycled from example 2.

FIG. 6 is the micro structure of the recycled powder from example 3 analyzed by EDS method.

FIG. 7 is the graph showing the quantity of electrons diffracted by the particular element during EDS studies from the powder recycled from example 3.

DESCRIPTION OF DISCLOSURE

The present disclosure relates to a process for recycling of tungsten carbide alloy comprising acts of oxidizing the tungsten carbide alloy to obtain tungsten oxide and other metallic oxides, grinding the tungsten oxide and other metallic oxides to obtain a powder and treating the powder with a carburizing mixture for reducing and carburizing the tungsten oxide and other metallic oxide powder to obtain the purified tungsten carbide alloy powder.

In an embodiment of the present disclosure, the oxidation is carried out in an oxidation furnace at a temperature ranging from about 400° C. to about 1000° C., preferably at about 950° C.

In still another embodiment of the present disclosure, the oxidation is carried out using oxidizing agent selected from a group comprising air and oxygen preferably air.

In still another embodiment of the present disclosure, the grinding is carried out by a method selected from a group comprising ball mill, Attritor Mill, High Speed Intensive mill; preferably ball mill.

In still another embodiment of the present disclosure, the grinding is carried out for a period ranging from about 0.5 h to about 10 h, preferably for about 2 h.

In still another embodiment of the present disclosure, the carburizing mixture is selected from a group comprising hydrogen, nitrogen, carbon monoxide, methane, carbon dioxide, compressed natural gas (CNG), liquefied petroleum gas (LPG) and mixtures thereof

In still another embodiment of the present disclosure, the carburizing mixture is a combination of about 10% liquefied petroleum gas and about 90% nitrogen

In still another embodiment of the present disclosure, the treatment with the carburizing mixture is carried out for a period ranging from about 1 h to about 15 h, preferably 3 h.

In still another embodiment of the present disclosure, the treatment with the carburizing mixture to obtain the purified tungsten carbide alloy powder is carried out in a reduction furnace at a temperature ranging from about 800° C. to about 1400° C., preferably at about 1050° C.

In still another embodiment of the present disclosure, the purified tungsten carbide alloy powder is cooled to a temperature ranging from about 300° C. to about 200° C. preferably about 200° C. in nitrogen, and then to about 35° C. to about 25° C., preferably about 25° C. in air.

In an embodiment of the present disclosure, the tungsten carbide alloy includes such physically diverse items as tungsten carbide alloy scraps, spent and off-quality wires, turnings, grindings, worn out inserts, drill bits, cutters, die blocks and any other forms of worn out machine tools which possess tungsten carbide alloy. Accordingly, for purposes of the present disclosure, the term “tungsten carbide alloy” is intended to include, but not be limited to, any and all of the various forms mentioned above.

In an embodiment of the present disclosure, recycling of tungsten carbide alloy includes recycling of tungsten carbide alloy, obtaining a pure form of tungsten carbide alloy powder from tungsten carbide alloy scraps. Accordingly, for purposes of the present disclosure, the term “recycling of tungsten carbide alloy” is intended to include, but not be limited to, any and all of the various forms mentioned above.

In an embodiment of the present disclosure, when compared to other processes for the recycling of tungsten carbide alloy from the worn out inserts and rejected products, the present disclosure is a very cost effective solution which yields the quality at par with virgin powders.

An embodiment of the present disclosure uses a thermo mechanical treatment which will convert the tungsten carbide back into mix powder with exactly same chemical composition as the mix produced from virgin powders and with other qualitative parameters which is ready to be pressed back into inserts. As the proposed process is a thermo mechanical process it does not generate any effluent.

In an embodiment of the present disclosure, the proposed process uses, simpler & cheaper machines and operations hence the cost of recycling is greatly reduced.

In another embodiment, the disclosure involves the oxidation of tungsten carbide scraps at a suitable temperature to convert the alloy elements into their oxides. The oxides are ground to convert them into powders. The oxide powders are mixed with reducing agents like carburizing gas and are reduced at a suitable temperature and environment, to convert back into original alloy powder mix.

In another embodiment of the present disclosure, the principle behind the disclosure is to convert the elements into their oxides which are very light and amenable to grinding. The oxide powders are then reduced to convert back into original elements. The carbon present in the tungsten carbide alloy as carbides will escape as carbon-dioxide during oxidation. This problem will be addressed using carbothermic reduction. This process can produce a high quality powder mix at a very cheaper rate by which the requirement for scarce, costlier virgin powders can be substituted, since the process is not calling for any costlier equipments or consumables.

In an embodiment of the present disclosure, during oxidation, tungsten oxide, cobalt-oxide and other metallic oxides are formed. In the process of reduction, which is a carbothermic process a carburizing atmosphere will be maintained with the help of hydrogen, nitrogen, carbon monoxide, methane, carbon dioxide, compressed natural gas (CNG), liquefied petroleum gas (LPG) and mixtures thereof.

The broad range of percentage of carburizing gas in the hydrogen mixture is 0.7% to 30%.

In another embodiment of the present disclosure, the oxidizing agent present inside the furnace chamber is air.

In an embodiment of the present disclosure, the final characterization of the tungsten carbide powder involves the following:

-   -   1. Chemical analysis to find out percentage of tungsten, carbon,         Cobalt & Oxygen using Electron Diffraction Studies;     -   2. Micro structural analysis (In mass production, this may not         be required)     -   3. Particle size analysis.

An embodiment of the present disclosure, is further illustrated by the following examples, which should not be construed to limit the scope of the disclosure in anyway.

Example 1

10 kgs of tungsten carbide alloy scrap was oxidized in air at atmospheric pressure at 950° C. for 10 Hrs. The oxidized powder was then ground in a ball mill for about 2 hours. This oxide powder was reduced and carburized concurrently by a carburizing mixture consists of 10% LPG and 90% Nitrogen for 6 hours at 1050° C. and cooled down to 200° C. in nitrogen and then room temperature in air.

TABLE 1 Comparative analysis of recycled powder with virgin powder of tungsten carbide alloy powder Recycled Virgin Element powder Powder Nickel 0.06 <0.3 Iron 0.30 <0.5 Molybdenum NIL <0.1 Chromium 0.18 <0.1 Titanium + 1.76 1 to 10 Tantalum + Niobium Cobalt 10.57 5 to 25 Tungsten Carbide Bal Balance Carbon 24.55 Min 6.1 Oxygen 0.02 <0.08

FIG. 2 is the micro structure of the recycled powder from example 1 analyzed by EDS method. FIG. 3 is the graph showing the quantity of electrons diffracted by the particular element from the recycled powder extracted from example 1.

The table 2 shown below illustrates the results of the quantitative analysis of the recycled powder from experiment 1.

TABLE 2 ZAF Method Standardless Quantitative Analysis Fitting Coefficient: 0.2972 Element (keV) Mass % Error % At % K CK* 0.277 24.55 0.16 54.42 3.2713 OK 0.239 0.02 0.25 10.02 3.5475 TiK 4.508 1.76 0.18 1.63 1.4256 CrK* 5.411 0.18 0.18 0.18 0.1677 FeK* 6.398 0.30 0.20 0.31 0.3759 CoK 6.924 10.57 0.27 8.58 10.5066 NiK* 7.471 0.06 0.26 0.02 0.0276 WM 1.774 62.56 0.33 24.84 46.7524 Total 100 100

Example 2

10 Kgs of tungsten carbide alloy scrap was oxidized in air at atmospheric pressure at 950° C. for 10 Hrs. The oxidized powder was then ground in a ball mill for about 2 hours. This oxide powder was reduced and carburized concurrently by a carburizing mixture consists of 10% LPG and 90% Nitrogen for 2 hours at 1050° C. and cooled down to 200° C. in nitrogen and then room temperature in air.

TABLE 3 Comparative analysis of recycled powder with virgin powder of tungsten carbide alloy powder Recycled Virgin Element powder Powder Nickel 0.30 <0.3 Iron 0.11 <0.5 Molybdenum NIL <0.1 Chromium 0.04 <0.1 Titanium + 1.82 1 to 10 Tantalum + Niobium Cobalt 8.67 5 to 25 Tungsten Carbide Bal Balance Carbon 5.2 Min 6.1 Oxygen 19.36 <0.08

FIG. 4 is the micro structure of the recycled powder from example 2 analyzed by EDS method. FIG. 5 is the graph showing the quantity of electrons diffracted by the particular element from the recycled powder extracted from example 2.

The table 4 shown below illustrates the results of the quantitative analysis of the recycled powder from experiment 2.

TABLE 4 ZAF Method Standardless Quantitative Analysis Fitting Coefficient: 0.2929 Element (keV) Mass % Error % At % K CK* 0.277 5.20 0.18 19.80 1.0686 OK 0.525 19.36 0.27 55.33 12.3928 TiK 4.508 1.82 0.14 1.74 1.5931 CrK* 5.411 0.04 0.18 0.04 0.0417 FeK* 6.398 0.11 0.20 0.09 0.1178 CoK 6.924 8.67 0.24 6.73 9.0186 NiK* 7.471 0.30 0.29 0.23 0.3274 WM 1.774 64.50 0.30 16.04 54.1903 Total 100 100

Example 3

10 Kgs of tungsten carbide alloy scrap was oxidized in air at atmospheric pressure at 950° C. for 10 Hrs. The oxidized powder was then ground in a ball mill for about 2 hours. This oxide powder was reduced and carburized concurrently by a carburizing mixture consists of 10% LPG and 90% Nitrogen for 3 hours at 1050° C. and cooled down to 200° C. in nitrogen and then room temperature in air.

Analysis of the carburized and reduced powder revealed that the reduction was complete and the carbon content was found at 6.3% which is the correct stochiometric composition. Further Cobalt found at around 9%, titanium found at 1.3% which confirms to the requirements of a ready to press Tungsten Carbide powder.

TABLE 5 Comparative analysis of recycled powder with virgin powder of tungsten carbide alloy powder Recycled Virgin Element powder Powder Nickel 0.03 <0.3 Iron 0.37 <0.5 Molybdenum NIL <0.1 Chromium 0.18 <0.1 Titanium + 1.64 1 to 10 Tantalum + Niobium Cobalt 11.63 5 to 25 Tungsten Carbide Bal Balance Carbon 6.28 Min 6.1 Oxygen 0.05 <0.08

FIG. 6 is the micro structure of the recycled powder from example 3 analyzed by EDS method. FIG. 7 is the graph showing the quantity of electrons diffracted by the particular element from the powder extracted from example 3.

The table 6 shown below illustrates the results of the quantitative analysis of the recycled powder from experiment 3.

TABLE 6 ZAF Method Standardless Quantitative Analysis Fitting Coefficient: 0.2931 Element (keV) Mass % Error % At % K CK* 0.277 6.28 0.20 24.33 1.2701 OK 0.325 0.05 0.10 10.11 6.5319 TiK 4.508 1.64 0.16 1.59 1.4182 CrK* 5.411 0.18 0.17 0.18 0.1677 FeK* 6.398 0.37 0.22 0.31 0.3759 CoK 6.924 11.63 0.27 9.18 11.9779 NiK* 7.471 0.03 0.26 0.02 0.0276 WM 1.774 79.82 0.33 54.28 53.8427 Total 100 100 

1. A process for the recycling of tungsten carbide alloy comprising acts of: a) oxidizing the tungsten carbide alloy to obtain tungsten oxides and other metallic oxides; b) grinding the tungsten oxides and other metallic oxides to obtain a powder; and c) treating the powder with a carburizing mixture for reducing and carburizing the powdered tungsten oxides and other metallic oxides to obtain the purified tungsten carbide alloy powder.
 2. The process as claimed in claim 1, wherein the oxidation is carried out in an oxidation furnace at a temperature ranging from about 400° C. to about 1000° C., preferably at about 950° C.
 3. The process as claimed in claim 1, wherein the oxidation is carried out using oxidizing agent selected from a group comprising air and oxygen, preferably air.
 4. The process as claimed in claim 1, wherein the grinding is carried out by a method selected from a group comprising ball mill, Attritor Mill, High Speed Intensive mill; preferably ball mill.
 5. The process as claimed in claim 1, wherein the grinding is carried out for a period ranging from about 0.5 h to about 10 h, preferably for about 2 h.
 6. The process as claimed in claim 1, wherein the carburizing mixture is selected from a group comprising air, hydrogen, nitrogen, carbon monoxide, methane, carbon dioxide, compressed natural gas (CNG), liquefied petroleum gas (LPG) and mixtures thereof.
 7. The process as claimed in claim 6, wherein the carburizing mixture is a combination of about 10% liquefied petroleum gas and about 90% nitrogen.
 8. The process as claimed in claim 1, wherein the treatment with the carburizing mixture is carried out for a period ranging from about 1 h to about 15 h, preferably 3 h.
 9. The process as claimed in claim 8, wherein the treatment with the carburizing mixture to obtain the purified tungsten carbide alloy powder is carried out in a reduction furnace at a temperature ranging from about 800° C. to about 1400° C., preferably at about 1050° C.
 10. The process as claimed in claim 9, wherein the purified tungsten carbide alloy powder is cooled to a temperature ranging from about 300° C. to about 200° C. preferably about 200° C. in nitrogen, and then to about 40° C. to about 20° C., preferably about 25° C. in air. 